France have been scoring for fun so far in this World Cup: three goals against Honduras and five against Switzerland. It could even have been five in the first game and eight in the second as they created so many chances overall with sharp, fluid and quick offensive moves.

However, Didier Deschamps knows that, even in the most attacking World Cup since 1970, Les Bleus will only go far in the competition if they have a strong defence. You win nothing (just ask the English and the Spanish) if you don't have a strong back four. The proof is there in history: France were crowned champions in 1998 after conceding just two goals in the whole tournament; Italy in 2006 and Spain in 2010 followed suit.

If the French hope to repeat the trick, they will have to button down for the rest of the tournament, as Deschamps' men have already conceded two goals, both against Switzerland. Even then, they were up 5-0 and switched off in the last 15 minutes -- you can put that down to a lack of concentration as the game was won anyway, or maybe of a lack of experience as well, but there is nothing to worry about.

One slight cause for concern going into the knockout stages is that the French have not been tested defensively so far. No offence to Carlo Costly and Jerry Bengtson, the Honduran strikers, or to Haris Seferovic, their Swiss counterpart, but they were never going to represent a real threat up front. Indeed first-choice centre-back pairing Raphael Varane and Mamadou Sakho looked very strong in those two games.

You tend to forget quickly that Varane is only 21 years old; he plays with so much maturity that you could easily think he is five or six years older. His touch is great, and his reading of the game is fantastic. There is no doubt that he will be, at some stage, one of the best centre-backs in the world, although there are fears about his fitness. His season with Real Madrid has been hampered by knee problems, and he is going to miss the game against Ecuador on Wednesday because of a stomach bug. He is fragile physically, and the problem is that Sakho is as well. He missed three months of action after Christmas with Liverpool because of a hamstring injury, then felt his thigh again against Switzerland last week and had to come off halfway through the second half as a precaution. Even though he should be fit enough to start on Wednesday, there are some worrying signs.

Furthermore, Varane and Sakho are one of the least experienced pairs of centre-backs in this competition. Varane has only eight caps, and Sakho does only slightly better with 21. You wonder how they would react in a high-pressure game against a top striker playing on a top team, and that is exactly what they will be tested with in the latter stages.

It is interesting to see that Deschamps is leaving Laurent Koscielny on the bench. The Arsenal defender was an important player for the manager in the WC qualifiers and has played 14 of his 18 caps under Deschamps, since the former Marseille coach took over two years ago. But everything changed when Koscielny was red-carded in Ukraine in the World Cup playoff first leg back in November. Deschamps was angry and disappointed with him after the 2-0 loss; Varane and Sakho came in, played the second leg and sealed qualification by overseeing a 3-0 win in which Sakho remarkably scored twice.

Some find it hard to believe Sakho is preferred to Koscielny, and it's easy to see why. Koscielny had a great season with the Gunners; he is solid and quick, reads the game well and has pace. Deschamps sees things differently, though. In Varane, he sees the future and the next Laurent Blanc. In Sakho, he sees a leader and the next Marcel Desailly. Indeed he even made Sakho France's vice-captain to show how highly he rates him.

In the centre of defence, France are lucky to have three strong players -- and don't forget Eliaquim Mangala, who has big potential as well. It is a luxury for Deschamps to have to choose between those four players, but the story is different for the full-backs.

Vice-captain Mamadou Sakho deserves his place after getting France to Brazil.

On the right, Newcastle's Mathieu Debuchy has started the first two games, ahead of new Manchester City signing Bacary Sagna, and has been good offensively. He has the freedom to go forward a lot, especially as Valbuena, who often starts in front of him on the right, likes drifting a lot in the centre and left. But Debuchy has not been good enough defensively in this tournament, and it's a worry considering the teams France have faced so far.

It will get tougher, and he might not be able to cope when the bigger teams arrive. Switzerland targeted him, and their best chances (and goals) came from his side. Debuchy is certainly less protected than Patrice Evra on the left. The Manchester United defender has Blaise Matuidi in front of him, which is equal to having three players given how much the PSG man runs! Debuchy has Paul Pogba ahead of him, and Pogba doesn't defend much, which makes Debuchy all the more vulnerable to attacks.

Evra is 33, and you can tell that on the pitch. He is not as sharp as he used to be, as we saw also in a poor season with Manchester United, but at least he has experience that compensates his current level of form. The only other alternative is Lucas Digne, who is just 20, didn't play much this season with PSG and has only two caps with France. Playing him in the latter stages would be a massive gamble.

That said, Digne will start against Ecuador and Antonio Valencia on Wednesday, which will be a tough task but offers him a chance to showcase his skills. It will be very interesting to see how he performs, but to know the real defensive value of this France team, we will have to wait a bit longer.